Rewrite extendDpathXX, no need to store whole Dpath objects
Rewrite extendDpathXX, no need to store whole Dpath objects

Revert back to the original approach and only store x-coordinates in V
instead of whole Dpath objects. Return previous k-value instead of
previous Dpath object. Now client code needs to track that itself again
but algorithm gets lighter.


znerol/node-delta,znerol/node-delta,znerol/node-delta